This fixes a panic I randomly ran into whilst mistyping in the command
palette: I accidentally ran `pane: swap item right`in a state where no
items were opened in my active pane. We were checking for `index + 1 ==
self.items.len()` there when it really should be `>=`, as otherwise in
the case of no items this panics.
This PR fixes the bug, adds a test for both the panic as well as the
actions themselves (they were untested previously). Lastly (and mostly),
this also cleans up a bit around existing actions to update them with
how we generally handle actions now.
Release Notes:
- Fixed a panic that could occur with the `pane: swap item right`
action.
e6267c42f7